Regulation And Optimization Of Band Structure And Electronic Properties Of Titanium Dioxide-Based Functional Materials

In recent years,titanium dioxide（TiO₂）has attracted extensive attention both experimentally and theoretically due to its application potential in areas such as clean energy acquisition and environmental protection.Pure anatase phase TiO₂ itself has many advantages,such as n-type conductivity,photocorrosion stability,non-toxic and abundant content,and high catalytic activity.However,its wide bandgap（3.2 e V）reduces its visible light region（45%of sunlight energy）where it absorbs sunlight adequately;In addition,the photogenerated electron-hole recombination effect of pure anatase phase TiO₂ is easy to occur,resulting in the inability of most photogenerated carriers to migrate to the surface of organic matter for reaction,affecting the reaction efficiency of photocatalysis.Therefore,in order to reduce the band gap value of pure anatase TiO₂,improve its light absorption in the visible light wavelength range,limit or reduce the probability of recombination effect,and improve the photocatalytic efficiency,domestic and foreign scholars have carried out various modifications to TiO₂Research.Among various modification methods,metal doping can successfully overcome the above deficiencies,thereby effectively improving the photocatalytic efficiency of TiO₂,but many metal doping studies only focus on doping of 3d transition metal elements,and there is still a lack of systematic research on 4d transition metal element doped TiO₂.In this paper,based on the first-principles calculation method under density functional theory,GGA+U calculations were used to study the effects of two control and optimization methods,4d transition metal element doping and oxygen vacancy defect,on the band structure and electronic properties of TiO₂.Therefore,we have a clear understanding of the modification method of the defects of anatase phase TiO₂ functional materials,and provide theoretical support for promoting the development and large-scale application of TiO₂ semiconductor photocatalytic functional materials.（1）Firstly,the theoretical calculation cutoff energy is 400e V and the kpoints is 5×5×2,the theoretical equilibrium lattice constant of pure anatase TiO₂calculated by GGA（U=0）is a=b=3.829（?）、c=9.769（?）,and is close to the experimental values a=b=3.785（?）、c=9.512（?）,various parameters and properties of pure anatase TiO₂ were calculated by the GGA+U（U=1,..,10）method（including lattice constant,band gap,formation energy,etc.）,which can lay the foundation for the next study of supercell TiO₂ with 4d metal element doping and oxygen vacancy defects.（2）Secondly,the supercell model used for 4d transition metal doped TiO₂ was constructed,the U value in the GGA+U calculation was determined for different element doping,and the 4d transition metal doping was divided into three types of doping characteristics according to the doping calculation results.Select one element doping for each type of characteristics to carry out systematic analysis and research,the reasonable choice of U value for GGA+U calculation of n-type Mo-doped TiO₂ should be1-3 e V,Mo-doped TiO₂ material is expected to become a relatively excellent light source Catalytic functional materials;for p-type Y-doped TiO₂,the results show that the electronic properties of the doped system have not changed,and the band gap has not been significantly reduced,and the photocatalytic effect of a single Y-doped TiO₂ is not ideal;for Tc-doped TiO₂The result with a U value of 3 is more suitable.At this time,the lower gap is smaller than the upper gap,which can improve the light absorption of visible light,which is beneficial to the photocatalytic process.（3）Thirdly,when doping TiO₂ with 4d metal elements,metal doping of different valences will introduce oxygen vacancies,and for anatase phase TiO₂ oxide,due to its own crystal structure characteristics,there are oxygen vacancies in itself,so research the interaction between doped metal and oxygen vacancies is very necessary.Therefore,the influence of the presence of oxygen vacancies on the energy band structure and electronic properties of Mo-doped TiO₂ is comparatively studied.The results show that the system band of Mo+Vo-doped TiO₂ are more intermediate states in the gap,and the gap state is more uniform in the energy band distribution,which can explain that the incorporation of Mo+Vo vacancy clusters can significantly improve the photocatalytic activity of TiO₂ under the experiment,this suggests that Mo doping and oxygen vacancy defects play a synergistic role.The formation energy calculation shows that Mo doping is more likely to occur in the experiment,that is Mo doping is more stable than Mo+Vo doping;at the same time,the effect of oxygen vacancies on doped metal ion TiO₂ under different Y doping concentrations is studied.The effect of energy band structure and electronic properties of Y+Vo doping compared with a single Y doping case makes the band gap appear an intermediate state,but does not change the electrical properties of the system,Y+Vo+Y doping makes the intermediate state disappear,and the fermi level is shifted to VB,the Y+Vo+Y cluster is the most likely combination of doping and defects in the Y-doped TiO₂ supercell,and this arrangement helps to provide the correct direction for the experimental research of Y-doped TiO₂.（4）Finally,the research summary of this paper is carried out,and the outlook for inadequacies in the research process.